ASNT Radiographic Testing Practice Test 2025 - Free Nondestructive Testing Practice Questions and Study Guide

The average gradient on the characteristic curve of a film is defined as the slope of the straight line joining two specified densities. This concept relates to how the film responds to changes in exposure to radiation, where the slope indicates the sensitivity and contrast of the film.

When measuring the average gradient between two points on the characteristic curve, the values of the optical density at those points are used to calculate how much the density changes with a change in exposure. A steeper slope reflects a greater change in optical density for a given amount of exposure, which signifies higher sensitivity and contrast in the film.

This understanding is crucial in radiographic testing because it helps technicians determine the appropriate exposure for achieving the desired image quality. The other options, such as exposure time, film's speed, and development time, are related to the overall imaging process but do not directly define the average gradient on the characteristic curve.